The present invention relates to clutch discs of friction type clutches.
A clutch of an automobile disconnects and reconnects the engine from the transmission and the drive line. A clutch disc of a friction type clutch is provided with a damper mechanism for isolating the vibration caused by variation in engine output torque from the transmission. That is, damper springs are mounted circumferentially around a flange of a spline hub and compressed circumferentially between the hub flange and an assembly of a clutch plate and a retaining plate. These damper springs do not have the same spring characteristic, but they are classified into groups having different spring characteristics, such that the overall spring characteristic changes in a sequence of stages in accordance with the relative angular displacement occurring between the hub flange and the clutch plate assembly. A maximum relative rotational angle within which the hub flange and the clutch plate are allowed to relatively displace is made as large as possible in order to obtain a good damper effect.
In a conventional design of such a torsion damper mechanism, the damper springs have approximately the same diameter, and are placed in series on the same circle. This arrangement limits the space for accommodating the damper springs, and limits, also, the relative rotational angle between the hub flange and the clutch plate assembly to under about 11 degrees. In order to increase the relative rotational angle beyond this limit, it is necessary to form, in the hub flange, large openings for accommodating the damper springs, but such a large opening size weakens the hub flange and causes excessive stress in the damper springs. Because of this 11-degree limit, a clutch disc of the conventional type can not sufficiently absorb torque fluctuation. This torque fluctuation produces gear noise due to backlash in the transmission, especially at low rotational speed and at idling.